40 



BULLETIN 1134, U. S. DEPARTMENT OF AGRICULTURE. 



COMPARISON OF CROSS-POLLINATION WITH RELATED AND WITH UNRELATED 



POLLEN. 



Flower buds on several Pima cotton plants in 1914 were emascu- 

 lated and bagged in the evening and were pollinated the following 

 morning, some with pollen from other plants of the same variety 

 and others with pollen of the Gila variety of Egyptian cotton. The 

 results, which show no significant difference in fertilization from the 

 two pollinations, are given in Table 21. 



Table 21. — Fertilization of emasculated Pima flowers resulting from cross- 

 pollination with pollen of the same variety and with pollen of the Gila 

 variety of Egyptian cotton-. 



Cross-pollination with- 



Number of 



bolls 

 matured. 



Mean 

 number of 

 seeds per 



boll. 



Pima (Egyptian) pollen. 

 Gila (Egyptian) pollen. . 



157 



15. 8± 0.48 

 15. 6± .36 



Difference. 



,2± .60 



A similar experiment was performed in 1917 on plants of a Pima 

 family which had been strictly inbred during three successive gen- 

 erations. The cross-pollinations of emasculated flowers were made 

 with pollen from (1) sister plants of the same inbred family, (2) 

 plants of the continuously open-pollinated stock of the Pima variety, 

 and (3) plants of the Gila variety. Table 22 gives the results of 

 this experiment, which show that while a greater number of seeds 

 per boll resulted from the application of pollen of another variety 

 of the Egyptian type as compared with that from pollen of related 

 and of unrelated plants of the same variety, the differences were not 

 significant. It may be concluded, therefore, that within the limits 

 of the Egyptian type there is no important difference in the compati- 

 bility of pollen derived from sister plants of a presumably homo- 

 zygous strain, from unrelated plants of the same variety, and from 

 another variety. 



Table 22. — Fertilization of emasculated Pima flowers resulting from cross- 

 pollination with pollen from sister plants and from unrelated plants of the 

 same variety and ivith pollen of the Gila variety. 



Cross-pollination with pollen from— 



Flowers 

 treated. 



Percent- 

 age of 

 bolls 



matured. 



number 

 of seeds 

 per boll. 



Sister plants of the Pima variety , 



Unrelated plants of the Pima variety , 

 Plants of the Gila (Egyptian) variety 



98±1.2 

 99± .7 

 97±2.1 



15.9±0.29 

 16. 3± .19 

 17. 1± .36 



Experiments will be described next in which cross-pollination 

 within the Pima variety was compared with cross-pollination with a 

 wholly different type, the Acala variety of upland cotton. The re- 

 sults of such an experiment, performed in 1920, are presented in 

 Table 23 (upper part) and indicate that the mean number of. seeds 

 per boll and the germination percentage of the seeds were signifi- 

 cantly higher from flowers which had received pollen of the other 





